This application is a 371 of PCT/EP98/06883 filed Oct. 30, 1998 which claims priority from Germany application No. 19748989.3 filed Nov. 6, 1997.
The present invention relates to an optical transmitting/receiving module.
For reasons of interference immunity as well as to minimize weight and volume, optical signal transmission is becoming increasingly important in comparison to signal transmission over electrically conductive connections. In this context, a significant proportion is constituted by optical waveguides such as glass fibers or plastic optical fiber cables. However, in optical data buses, in contrast to electrical data buses, supplemental optical transmitting and receiving modules are required as electrical/optical or optical/electrical converters, since signal processing in the stations still takes place electrically. As a result, additional costs are created, and volume and weight are increased. Depending on the bus topology and bus protocol, in line-conducted optical systems for the transmitting and receiving paths, both two light waveguides (so-called two-wire arrangement) as well as one light waveguides (so-called one-wire arrangement) are used. The advantage of a one-wire arrangement is that a minimal number of lines and plug-in connections are used in the physical bus layer, although in the optical transmitting/receiving module, coupling elements such as Y-couplers also have to be integrated, which cause additional transmission losses.
From German Patent Document No. 33 15 861 A1, a fiber-optic coupler is described for connecting a light waveguide to a transmitting/receiving terminal. A support module for a transmitting and a receiving element contains a support body made of optically transparent material. The end segment of a light waveguide is inserted into a V-shaped groove on the support body. The groove terminates in a semi-transparent inclined plane, which functions as a transmitting/receiving deflector. Light arriving in the light waveguide is directed by the semi-transparent mirror surface through the material of the support body onto a receiving element. Light emitted by a transmitting element is deflected at the mirror surface into the light waveguide.
Since the support body at the deflecting mirror surface must be semi-transparent, the selection of materials is limited to transparent ones. In this context, the total coupling efficiency as the product of the coupling and decoupling efficiency, is less than 25%.
From the document, W. Hunziker, et al.: IEFE Photonics Technology Letters, Vol. 7, No. 11, November 1995, a method is described for housing a semiconductor laser array in silicon in connection with optical waveguides.
In addition, International Patent Document WO 97/36201 A describes a transmitting module, in which light from a transmitter is deflected into a transmission fiber with the assistance of a reflectively coated, opaque support plate, and light is directed from a receiving fiber to a receiver also with the assistance of a support plate.
In this context, a significant disadvantage lies in the use of silicon as the support material, which must be structured/shaped in relatively expensive process steps. Furthermore, the procedure described in the document is limited, in the creation of grooves, to the use of mono-crystalline (111) silicon and therefore represents a comparatively cumbersome and thus expensive mode of operation, restricting the range of variation in the selection of materials.
Therefore, an object of the present invention is to indicate an optical transmitting/receiving module that is distinguished by an optimized arrangement for increasing the efficiency in the signal processing and by a compact design, and that has a simple shape, making it therefore cost-effective and allowing for a wide range of variation in the selection of materials.
The present invention provides an optical transmitting/receiving module, in particular for a one-wire arrangement, comprising a reflectively coated, opaque support plate, optical transmitting/receiving fiber(s), a transmitter as laser diode, and a receiver. A groove, introduced in the reflectively coated surface for accommodating the transmitting/receiving fiber, is arranged on the support plate, and a coupling mirror, as an extension thereof, is stamped on the support plate. The coupling mirror only partially blocks the fiber end, its inclination being determined as a function of the choice of mode, at a defined angle for the maximum coupling of the light. A decoupling mirror, as a further extension, is stamped on the support plate, the decoupling mirror completely blocking the fiber end. The optical transmitter and receiver may be mounted directly over the mirrors (FIG. 3a).
One embodiment of the optical transmitting/receiving module is composed of a support plate, a transmitter, a receiver, and optical fiber(s), and can be used for a two-wire arrangement or a one-wire arrangement having a supplemental Y-coupling element or for a one-wire arrangement without the supplemental Y-coupling element. The basic element of this arrangement is a metallic or plastic support plate, which has a reflective coating and is therefore opaque, and deflecting mirrors having adjustable inclination, area, and surface quality for deflecting the light to be coupled or decoupled, as well as recesses for accommodating the transmitters or receivers are stamped into grooves that are created using stamping technology, for example V- or U-shaped or rectangular grooves, for accommodating multimode optical fibers. For the opaque reflective coating on the support plate, a gold coating, for example, can be used.
As the optical transmitter, it may be particularly suitable to use a surface-emitting laser diode having a vertical resonator (VCSEL; vertical cavity surface emitting laser) in connection with a photo diode as the receiver. The transmitting/receiving fibers are composed of cylindrical multimodule light waveguides made of glass or polymers, having a core diameter of at least 50 xcexcm.
In the case of a two-wire arrangement or a one-wire arrangement having a supplemental Y-coupling element, on the one hand, two separated grooves, introduced using stamping technology for accommodating the transmitting and receiving optical fibers, and two separated coupling and decoupling mirrors are stamped on the support plate, and the optical transmitter and receiver are disposed directly over the mirrors in pre-stamped recesses.
In the case of a two-wire arrangement or a one-wire arrangement having a supplemental Y-coupling element, on the other hand, two separated grooves, introduced using stamping technology in the reflectively coated surface for accommodating the transmitting and receiving optical fibers, are stamped in the support plate, and a housed optical transmitter and a receiver are disposed in pre-stamped recesses in direct extension of the fibers.
Furthermore, in the case of a one-wire arrangement without supplemental coupling elements, a groove introduced using stamping technology in the reflectively coated surface for accommodating the transmitting/receiving fibers, a coupling mirror as an extension thereof, only partially blocking the fiber end, and a decoupling mirror as a further extension completely blocking the fiber end are stamped on the support plate, and the optical transmitter and receiver are disposed directly over the mirrors in pre-stamped recesses.
Alternatively, the optical transmitter is arranged in a pre-stamped recess directly over the mirrors and, in a further extension of the fiber, the optical receiver is disposed directly behind the coupling mirror in pre-stamped recesses.
The stamping technology used can also be applied if, in place of VCSEL and photo diode chips, housed transmitters and receivers are used. Also possible is a combination of housed and non-housed components.
One advantage of the present invention, and particularly efficient, is the fact that by using stamping technology, in which the desired structure is stamped into the surface of the support plate using a stamp die, a cost-effective, compact design is achieved.
A further advantage of the present invention lies in the fact that, for example, coupling elements having minimal installation losses are also integrated in the stamped support plate of the module, so that compact, low-loss transmitting/receiving modules are available for data buses in a one-wire arrangement. As a result of an arrangement in which the components fiber, transmitter, and receiver, lie one behind the other, supplemental Y-coupling elements can be dispensed with, as result of the fact that the coupling mirror blocks only a certain part of the light that emerges from the transmitting/receiving fiber. The unblocked component is coupled onto the detector. As result of the proposed stamping technology, it is possible to optimize the height and angle of the coupling mirror with regard to the maximum coupling of the light of a preselected transmitter into a preselected fiber. As a result of optimization, overall efficiencies significantly greater than 25% can be achieved.